21991312 has 40 divisors (see below), whose sum is σ = 50818176. Its totient is φ = 9014016.

The previous prime is 21991301. The next prime is 21991313. The reversal of 21991312 is 21319912.

It is a Harshad number since it is a multiple of its sum of digits (28).

It is not an unprimeable number, because it can be changed into a prime (21991313) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1693 + ... + 6844.

Almost surely, 2^21991312 is an apocalyptic number.

It is an amenable number.

21991312 is an abundant number, since it is smaller than the sum of its proper divisors (28826864).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21991312 is a wasteful number, since it uses less digits than its factorization.

21991312 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8575 (or 8569 counting only the distinct ones).

The product of its digits is 972, while the sum is 28.

The square root of 21991312 is about 4689.4895244579. The cubic root of 21991312 is about 280.1670431822.

The spelling of 21991312 in words is "twenty-one million, nine hundred ninety-one thousand, three hundred twelve".